Question:

I'm learning functional programming and try to apply its ideas in day job with imperative languages. My favourite idea is data immutability. I can apply this concept in my programs and try to make all my data structures and model objects immutable. But I have a standard feature in my app: edit user profile. So, I got profile data from the server and create an immutable domain model of it: class UserProfile and show its info to the user. User can edit any fields: change name, surname, age, interests, whatever. The first idea is to make UserProfile global, mutable and create a setter for each field. But I want to handle this logic in a pure functional way.

So, what are the possible ways of handling this logic correctly in a functional way?

Answer:

You might find the Updatable type from mvc-updates useful. The basic idea is that you build an Updatable value by supplying a concurrent input (i.e. a Controller) and a Fold over that input:

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